时差N小时 锋利的刀刃有何特别之处?(下)（在线收听）

First hold the nail with the wide head by its shaft and push it head-first into the ball of clay. Then do the same with the small-headed nail.

首先将宽头钉的杆竖起，将其头朝下推入橡皮泥球。然后对窄头钉再重复一次。

The small-headed nail goes into the clay much more easily than the wide-headed nail. Since the head of the small nail has less surface area than the big one, the force of your push is concentrated in a smaller area, exerts more pressure on the clay, and so the nail goes in more easily. The same principal causes pointed high-heeled shoes to sink into a soft surface more easily than flat shoes.

窄头钉比宽头钉更容易嵌入橡皮泥。由于窄头钉的头部面积比宽头钉小，你的推力将集中在一个更小的区域，对橡皮泥产生更大的压力，因此钉子更容易嵌入。同理，尖高跟鞋比平跟鞋更易陷入表面柔软的物体。

By applying this principal to the knife you can see that with a keener edge there’s a greater concentration of the pressure on the edge, so it takes much less force to make the knife cut.

将这一原理运用在刀上，你会发现，刀刃越锋利，压力就会更加的集中，因此切割起来也更加省力。